Specific capture of magnesium ions by phosphorus atomic sites on self-floating nuclei advances Mg/Li separation in salt lakes brine

Efficient magnesium-lithium separation is a critical step in extracting lithium ions from salt lakes brine. Precipitation of Mg²⁺ from liquid to solid is the simplest separation method, but a side reaction of Li⁺ adsorption by precipitated floc leads to incomplete Mg/Li separation and lithium loss. In this study, we grafted phosphorus atomic sites onto silica-based nuclei with self-floating separation capability to prepare adsorbents with specific capture ability for Mg²⁺, achieving efficient Mg/Li separation from brine. Surface composition analysis shows that the content of P element is 0.99 %, which contributed 82.20 mg g⁻¹ of Mg²⁺ adsorption capacity of at room temperature. During this process, the content of Na and Ca elements in the material decreased by 1.47 % and 0.85 %, respectively, due to ion exchange and surface coverage. In samples of the same water quality as Smackover brine, the Li content in the Mg²⁺-captured material was only 3.20 % of that in directly precipitated Mg(OH)₂, due to the adsorption selectivity coefficient of the material for Mg²⁺ to Li⁺ reaching 62.26. The outcomes of this research enlighten the selective capture ability and mechanism of phosphorus atomic sites for Mg²⁺, providing new insights for efficient Mg/Li separation from salt lakes to improve raw brain grade.